This application is the national stage of International Application No. PCT/EP00/12759, filed Dec. 14, 2000, designating the United States.
Motor vehicles, which are equipped with an electronic system for controlling the driving dynamic, such as ABS, ASR or ESP, usually have a unit for measuring the angular velocity of the vehicle wheels. A measurement of the angular velocity of the vehicle wheels can especially take place with the aid of active wheel rpm sensors. It is already known that the monitoring of a change in the angular velocity of the wheels is suitable for tire pressure loss detection. For this purpose, some systems first store the detected wheel velocities in a memory and evaluate these wheel velocities at a later time point. Compared to systems which undertake no storage of data, a conclusion can be drawn as to the actual driving situation from the trace of the wheel velocities so that fluctuations of the wheel angular velocities can be removed from the data which is necessary for an adequate accuracy of the pressure loss detection. The fluctuations of the wheel angular velocities are superposed on the tire pressure loss.
It is common for practically all known tire pressure detection systems that the detection system must first be advised when the desired rated pressure P0 of the mounted wheels is adjusted. This starting condition for the tire pressure detection can be told to the electronic system, for example, by means of a reset switch which must be pressed by the operator of the vehicle. If, after a specific time, a pressure loss occurs at one or more wheels, the tire pressure of the affected wheel drops by the pressure difference AP. As a consequence of the pressure loss, the dynamic rolling radius of the affected wheel changes in a characteristic manner dependent upon the tire. Usually, in known pressure loss detection systems, a pressure loss is detected when the dynamic rolling radius of the affected wheel has reduced by a specific minimum value.
Although many methods for detecting a pressure loss by evaluating the wheel velocity have been suggested, the need is still present to still more reliably and accurately carry out the pressure loss detection on the basis of wheel rpm information The problem in the pressure loss detection is to distinguish a change of the dynamic rolling radius based on a pressure loss from changes of the dynamic rolling radius which, inter alia, can be caused by dynamic driving situations, especially driving in a curve, acceleration, deceleration, et cetera and roadway effects (potholes, various friction values) and, as a rule, are greater than the influence of a pressure loss on the dynamic rolling radius (disturbance effects).
In order to realize a detection of pressure loss with increased accuracy, especially also in dynamic driving maneuvers, German patent application 199 61 681 suggests a method wherein additional physical data, such as yaw rate, acceleration, brake actuation, engine torque, et cetera are included in the detection algorithm so that a pressure loss detection can be carried out also during dynamic driving maneuvers (driving in a curve, acceleration, deceleration, et cetera).
In U.S. Pat. No. 6,439,045, a pressure loss detection method is described, which is integrated into an electronic anti-blocking system (ABS), wherein, after triggering the reset switch, when the rated pressure of the wheels is adjusted, first a time limited learning phase is run through in which a microcontroller follows wheel angular velocities while considering the driving situation and from the time-dependent trace of the reference values, upper and lower limit values (G1 and G2) are fixed. The reference values are formed from the wheel angular velocities. After the learning phase, a comparison phase starts in which a check is made as to whether the actual specific reference values lie within the range defined by the learned limit values.
The method considers the actual driving situation by excluding, during the learning phase and during the comparison phase, reference values during unsuitable dynamic driving situations.
Known methods are limited in that a pressure loss detection can be carried out only during driving situations of low dynamics (for example, essentially during a straight line travel wherein no transverse or longitudinal acceleration acts on the vehicle).